1. Field of the Invention
The present invention relates to a light wave distance measuring apparatus, and method for determining the distance of an object from a reference point. In particular, the present invention is directed to a method and apparatus in which a light wave distance measurement is performed by determining a phase difference between a phase of a receiving signal, obtained by transmitting intensity-modulated light of a light-emitting element having a specific frequency, to a target, reflecting the intensity-modulated light to a light-receiving element, and between internal light of a predetermined phase obtained by "cutting-off" the intensity-modulated light received by the light-receiving element. By this method and apparatus, a distance from a reference point to the target is determined.
2. Description of the Prior Art
A conventional light wave distance measuring device, such as, for example, the light wave distance measuring device shown in FIG. 9, comprises a light-sending optical system 41 and a light-receiving optical system 42. The light-sending optical system comprises a light-sending element 43 that emits a light wave (beam), a condenser lens 45, and an optical fiber 47. The light-receiving optical system 42 comprises a light-receiving element 44, a condenser lens 46, and an optical fiber 48. The optical fiber 47 functions to transmit light emitted by the light-sending element 43. The optical fiber 48 functions to receive light to be directed to the light-receiving element 44.
Light (e.g., a light wave) from the light-sending optical system 41 is transmitted as an internal light to the light-receiving optical system 42 via a relay condenser lens 49 and a reflecting mirror 50. Further, light from the light-sending optical system 41 is additionally transmitted as an external light towards a target (object) via a reflecting prism 51 and an objective lens 52. That is, the external light is transmitted towards the object to which a distance from a reference point is measured.
Light reflected from the target is condensed by the objective lens 52, level-adjusted by a variable ND (neutral density) filter 53 having a density which continuously changes, and forwarded (transmitted) to the light-receiving optical system 42. Thus, a distance from a reference point to the object is determined based upon a phase difference of the internal and external light waves.
However, in the above-mentioned conventional light wave distance measuring device, a transmission circuit of the light-sending optical system 41 and a reception (receiving) circuit of the light-receiving optical system 42 should be separated (kept away) from each other, in order to prevent an occurrence of an electromagnetic wave induction. Thus, optical fibers are necessary. The use of optical fibers with the conventional measuring device increases the cost of the measuring device. Further, the treatment (manipulation) of light in both the light-receiving optical equipment 41 and the light-receiving optical equipment 42, and in particular, an angle adjustment of the internal light is complicated.
In addition, it is not possible to prevent losses in the amount of light that is transmitted, such loss occurring as a result of errors in the adjustment of the optical fibers 47 and 48, the relay condenser lens 49, and the reflecting mirror 50. Thus, the accuracy of a distance measurement using the conventional measuring device is reduced.